Mevastatin (also known as compactin) and lovastatin (also known as mevinolin) are naturally occurring HMG-CoA reductase inhibitors. These compounds have been used medicinally in the control of human serum cholesterol levels. Both compounds contain a (2S)-2-methylbutyryloxy substituent at the C-8 position of their hexahydronaphthalene nucleus and both produce medicinal analogues with increased potency towards HMG-CoA reductase when the aforementioned 2-methylbutyryloxy side chain is converted into a 2,2-dimethylbutyryloxy group. The analogue which is obtained from lovastatin by such a conversion is known as simvastatin. A method for the commercial scale production of simvastatin from lovastatin is the subject of the present invention.